1. Field of the Invention
The present invention relates to control of a storage system that comprises storage devices of a plurality of types.
2. Description of the Related Art
The storage system can be constituted by one or a plurality of storage subsystems (sometimes called simply ‘storage’ hereinbelow). A plurality of storage devices can be installed in the storage.
In a computer system in an enterprise or the like, the storage capacity of the storage also increases as the amount of data stored by the storage increases and as data is held for long periods. Further, in order to hold data for long periods, data must be archived by considering the warranty periods of the respective storage devices in the storage.
The adoption of a method that withdraws a storage device whose warranty period has expired by performing data migration to another storage device (a new storage device or a storage device whose warranty period has not yet been exceeded, for example) when the period over which the data stored in a storage device are archived is longer than the warranty period of the storage device may be considered. For example, a technology that compares the warranty period of a hard disk with the archive deadline of data, selects a hard disk for archiving data on the basis of the comparison result, and archives the data in the selected hard disk is disclosed in Japanese Patent Application Laid Open No. 2005-301684.
Furthermore, storage devices for archiving data include flash memory. Flash memory is generally said to have a long lifespan because, although there are restrictions on the write number, there is no accompanying motive power of drive rotation or the like in comparison with a hard disk. However, the bit costs of flash memory are, at the time this specification was written, higher than the bit costs of a hard disk.
In view of this fact, mixing a hard disk and flash memory as a plurality of storage devices in the storage system may be considered. When the technology of Japanese Patent Application Laid Open No. 2005-301684 is simply applied to such a storage system, the following problems can arise.
That is, because flash memory has a longer lifespan than a hard disk, there are a great number of opportunities for selecting flash memory for data archiving. However, because of the restrictions on the write number, there are cases where the lifespan of the flash memory eventually drops as the write number of the data of the flash memory increases.
Further, as mentioned earlier, the bit costs when data are stored are generally higher for flash memory than for a hard disk. In addition, bit costs are also incurred when data migration is performed from a certain storage device to another storage device. Hence, when data archiving is performed without considering the number of data migrations or the data archiving location and so forth, there is a risk of high costs being incurred in the data archiving.
The above problem can arise only when the storage devices of the plurality of types are a hard disk and flash memory.